Detection of early atherosclerosis in M. fascicularis with transcutaneous ultrasonic measurement of the elastic properties of the common carotid artery.

The elastic properties of 22 common carotid arteries from 13 male cynomolgus monkeys (M. fascicularis) that were fed either a high cholesterol (test) diet or a standard monkey chow (control) diet for 18 months were measured noninvasively with 5 MHz ultrasound. A B-mode image of the artery was obtained with a 32-element linear array transducer, and a single line of video ultrasonic information was selected for tracking the echoes from the adventitial side of the near wall to the lumen-intima interface of the far wall. This technique measured lumen diameter plus anterior wall thickness. The diastolic diameter (Dd) (mean +/- SEM) of the test arteries was slightly larger than controls (2.9 +/- 0.1 vs 2.5 +/- 0.1 mm), whereas the fractional diameter change from diastole to systole (DeltaD/Dd, where DeltaD = diameter change) was slightly less (0.062 +/- 0.010 vs 0.082 +/- 0.011). Direct subclavian artery pulse pressure (DeltaP) in the test animals (63 +/- 4 mm Hg) was significantly greater than in the controls (41 +/- 2 mm Hg), whereas there was no difference in diastolic pressure (85 +/- 3 vs 81 +/- 2), respectively. The pressure-strain elastic modulus Ep = (DeltaP/DeltaD) Dd was significantly greater in the test monkeys (182 +/- 33 kPa) than in the controls (73 +/- 9 kPa). Morphometric analysis of atherosclerosis revealed more connective tissue and intra- and extracellular lipids in the test arteries than in the controls. Based on the average of three cross-sections equally spaced along each common carotid artery, the intimal area and the maximal intimal thickness averaged 0.89 +/- 0.16 mm2 and 0.26 +/- 0.04 mm for the test monkeys compared to negligible intimae from the controls. Medial area also was significantly greater in the test monkeys (0.71 +/- 0.03 mm2) compared to controls (0.57 +/- 0.04 mm2). Percentage stenosis defined as intimal area/IEL area, where IEL area is that within the internal elastic lamina, showed the test arteries to have 30 +/- 5% stenosis compared to 0% for the controls. However, dilatation appeared to compensate for any loss in lumen area due to intimal thickening. In this study, significant carotid artery stiffening associated with diet-induced atherosclerosis is demonstrated. This noninvasive technique may be useful in pediatrics and in preventive medicine for the detection of arterial stiffening associated with early progressive atherosclerotic lesions.